1. Field of the Invention
The present invention relates to an ink jet head unit for recording information by droplets discharged from a discharging port, an ink jet head cartridge having the above-described unit and an ink jet recording apparatus having the above-described head cartridge.
More particularly, the present invention relates to an ink jet head unit, an ink jet head cartridge and an ink jet recording apparatus having a portion through which ink passes and a junction of the ink supply passage exhibiting improved sealing performance and air tightness performance.
2. Related Background Art
In order to perform a recording operation as desired in accordance with the ink jet recording method in which ink is discharged from a discharging port, air tightness must be satisfactorily secured in an ink passage and an ink supply passage.
As shown in FIG. 15, an example of an ink jet head (hereinafter sometimes called an "IJH") for use in the ink jet recording method comprises a substrate 1 (hereinafter called a "heater board") on which an ink discharging pressure generating device is formed, a liquid chamber 7 connected to the substrate 1 and accommodating a recording liquid (hereinafter called "ink") and a substrate 2 having a recessed portion which constitutes an ink passage 8. The above-described substrate 2 integrally has an orifice plate 4 (hereinafter called a "grooved ceiling plate") which has ink discharge port 9 communicated with the ink passage 8 and acting to discharge ink.
The heater board 1 is allowed to adhere to a supporting substrate 3 by an adhesive agent, while the grooved ceiling plate 2 is allowed to adhere to the surface of the heater board 1 in such a manner that a heater portion disposed on the heater board 1 and serving as an ink discharging pressure generating device coincides with the ink passage 8 formed in the grooved ceiling plate 2. Furthermore, the orifice plate 4, which is the grooved ceiling plate, is disposed on the front surface of the supporting substrate 3 in such a manner that it is downwardly hung.
Ink is supplied from an ink supply member 5 after it has passed through an ink supply port 2a formed in the upper portion of the grooved ceiling plate. The ink supply member 5 has a projection rod which is inserted into a through hole formed in the supporting substrate before they are caulked by heat so that the ink supply member 5 is secured to the supporting substrate.
It is necessary for an ink jet head unit of the above-described type in which the IJH is constituted by bringing the first substrate, on which the energy generating device is formed, and the second substrate having a groove, which forms the ink passage through which recording liquid passes through, into contact with each other in a hermetical manner by mechanical urging force to be arranged in such a manner that the first substrate and the second substrate are brought perfectly into contact with each other so as to be hermetically sealed from outside air. If the above-described air tightness is not realized satisfactorily, there arises a problem in that normal liquid discharge cannot be performed because ink placed in the IJH leaks outside or the pressure generated at the time of discharging the liquid droplet leaks through the ink passage or the like. However, it is extremely difficult to bring the above-described two substrates perfectly into contact with each other due to a limitation present at the time of reducing cost or the overall size because it is necessary for the accuracy of each element to be extremely improved and the mechanical urging force to be extremely enlarged.
The above-described air tightness must, of course, be sufficiently maintained even if pressure for discharging ink is repeatedly applied.
Furthermore, there is a necessity of sucking ink placed in the IJH by a cap member to be described later in a case where liquid cannot normally be discharged, for example, after the ink jet unit has been allowed to stand for a long time. Therefore, air tightness must be realized not only in the IJH but also the peripheral portion of the IJH.
As a method of improving the air tightness in the vicinity of the IJH, a structure has been disclosed in Japanese Laid-Open Patent Application No. 2-121841 which is arranged in such a manner that a silicon sealer is introduced into small gaps 10a and 10b between the ink supply member 5, the heater board 1 and the grooved ceiling plate 2 and the like. Furthermore, the same is introduced into an adhesive space in the connecting region to which the adhesive is introduced and which has small gaps formed between the orifice plate and the front surface of the supporting substrate.
Furthermore, the above-described sealer acts to seal a connecting portion 10c for establishing a connection between the heater board 1 and the grooved ceiling plate. The same also acts to seal the connecting portion of the ink supply member 5 and the connecting portion 10d to be connected to the ink supply port 2a which is the connecting portion with the ink jet head. However, it is not used in a case where the ink supply member 5 and the grooved ceiling plate 2 are integrally formed. That is, the sealer is used as follows:
(1) It acts to uniformly seal a very small gap formed in a connecting region positioned between the orifice plate 4 and the front surface of the supporting substrate 3 and the gaps 10a and 10b formed between a head chip constituted by the heater board 1, the supporting substrate 3 and the groove ceiling plate 2 and the ink supply member 5. As a result, it forms and remains a sealed space which is sufficiently large to perform the recovery operation by sucking in order to overcome a problem of non-discharge from the ink discharge port 9 due to blinding caused from solidification of dried ink or bubbles mixed into the ink passage 8 or the like.
(2) It is used to seal the connecting portion 10c between the heater board and the grooved ceiling plate 2 and the connecting portion 10d formed between the ink supply member 5 and the ink supply port 2a.
Furthermore, the sealer also acts to protect the wire bonding portion for electrically connecting the printed circuit board and the IJH from mechanical force generated due to impact or drop or moisture, the printed circuit board serving as a wiring portion for supplying electric energy with which the IJH is caused to discharge liquid.
On the other hand, the structure of the connecting portion (10d) of the ink supply passage for supplying ink to the IJH is arranged in such a manner that the force is applied to the connecting surface between the ink supply member 5 and the ink supply port 2a to improve the adhesion. Furthermore, the silicone resin sealer is used to improve the air tightness.
As an example of the above-described structure, a structure is employed in which the ink supply port of the IJH and the conducting pipe of the ink supply passage for supplying ink are brought into contact with each other in such a manner that the free end portion of the conducting pipe of the cantilever type is brought into contact with the ink supply port before the overall body is warped. As described above, force generated by deforming the members positioned adjacent to the connecting portion is usually utilized.
However, in the above-described case in which the members are warped, there arises a risk of breakage of the member if the members are warped excessively. Therefore, the above-described member such as the conducting pipe must have a predetermined length or longer. As a result, there arises a problem in that the size of the ink supply passage member including the conducting pipe formed into the above-described structure cannot be reduced.
In addition, since the connections of the members such as the conducting pipe and the ink receiving port brought into contact with each other are established by utilizing the warp or the like of the members, it is difficult to hermetically connect them. Furthermore, the sealer for sealing the members is undesirably introduced into the connecting portions or the ink can be allowed to leak due to the insufficient result of the sealing operation.
On the other hand, the silicon resin is used as the sealer to be injected into the above-described IJH portion and the connecting portion of the above-described supply passage. However, since the silicon resin displays a high gas permeability of 400.times.10.sup.-10 [cm.sup.3 ][cm]/[sec][cm.sup.2 ][cmHg] with respect to air, it is undesirably introduced into the IJH in a relatively short time in an atmospheric condition of low humidity. Therefore, the normal ink discharge cannot be performed, and, worst of all, the ink passage is blocked by bubbles formed by introduced air, causing a problem to be taken place in that the ink discharge cannot be performed.
Furthermore, since it well displays a high steam permeability of 4.times.10.sup.-6 [cm.sup.3 ][cm]/[sec][cm.sup.2 ][cmHg], ink which is placed at the front end portion of the nozzle and the main component of which is water can undesirably evaporated in a relatively short time. Therefore, the density of ink is raised and thereby the normal ink discharge is inhibited and, worst of all, ink discharge cannot be performed.
The above-described phenomenon shows a tendency in that it apparently arises in a state of high temperature or a state of low temperature. In order to overcome the above-described problem, a structure has been employed which is arranged in such a manner that the adhesion between the capping and the head is improved. Another structure is employed which is arranged in such a manner that material displaying a low steam permeability is employed as the material for the capping member. However, although a certain effect is obtained from the above-described structures, the degree of it has not been satisfactory. Therefore, a manual or an automatic recovery operation by means of sucking or a previous discharge for purging must be performed. In a case of the manual recovery operation, a problem takes place in that a user must frequently perform the recovery operations. In a case of the automatic recovery operation, another problem takes place in that a timer or the like for performing the automatic ink sucking sequence must be provided for the body of the printer. In addition, since the silicon resin displays a high gas permeability with respect to oxygen and nitrogen, air is undesirably introduced into the IJH in a short time and thereby the normal ink discharge operation cannot be performed. In an extreme case, the ink passage is blocked by bubbles formed by introduced air, causing the problem to be taken place in that the ink discharge cannot be performed. Therefore, the ink sucking operation must frequently be performed as the recovery operation.
The above-described deterioration in the ink due to the undesirable introduction of air or the evaporation of the solvent of the ink becomes critical in an ink jet head unit which uses an electrothermal converting material. The reason for this lies in that the change in the ink composition considerably affects the generation of the bubbles at the time of performing the ink discharge by generating the bubbles with heat.
The above-described problem becomes critical in a case of the IJH of the type arranged in such a manner that the two substrates are connected to each other by the mechanical urging force to form the ink passage and the common liquid chamber because the gap cannot completely be eliminated.
The above-described recovery operation performed frequently will decrease the number of sheets which can be printed for one cartridge because ink used for the above-described recovery operation is rejected as waste ink and the same is not used in the printing operation. As a result, the running cost cannot be reduced. Furthermore, since there arises a necessity of forming a space for accommodating the waste ink, the overall size of the printer must be enlarged by a degree corresponding to the above-described required space. The above-described becomes critical in an ink jet cartridge of a type which has the ink jet unit and the ink tank formed integrally because there is a desire to minimize the capacity of the ink tank and the overall size of the printer.
On the other hand, in a case where the material displaying low gas-permeability and a low steam permeability is used as the sealer, it corrodes the aluminum electrode or the aluminum wire bonding portion. Therefore, the above-described material cannot be used in a case where there is a risk of disconnection. That is, since aluminum is ampholytic metal, it can be corroded by acid and alkali. For example, aluminum can react on amines contained in an epoxy adhesive agent, peroxides contained in an acrylic adhesive agent, chlorine ion (Cl.sup.-), sodium ion (Na.sup.+) and potassium ion (K.sup.+) and the like.
Furthermore, the above-described sealer for use in the wire bonding portion and the portion around the IJH, as a member for covering the IJH, must have an excellent adhesive performance with a substrate made of polysulfone, polyphenylene oxide (PPO), aluminum or silicon. In addition, the sealer must protect the wire bonding portion from impact, vibrations or atmospheric change such as the temperature or moisture change. Therefore, it must be an elastomer displaying moisture resistance.